1. Field of the Invention
The present invention relates to a technology of forming a thin film in process of manufacturing a semiconductor device, and more particularly to a film forming ring capable of improving the burying characteristic when burying a fine recess of high aspect ratio with a thin film and a method of manufacturing a semiconductor device.
2. Description of the Related Art
Recently, in the trend of smaller size and higher density of a semiconductor element, there is an increasing demand for burying technology (thin film forming technology) having excellent burying characteristic, capable of burying a fine recess of high aspect ratio with a thin film without forming voids in the inside thereof. To meet such a need, for example, a so-called plasma CVD apparatus is being used. The technology relating to the plasma CVD apparatus is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 7-106316, 2001-7090, 2002-241946, and 2002-110646. The plasma CVD apparatus is capable of ionizing components of a film forming material (material gas) in the plasma state, and applying bias to a semiconductor substrate. Accordingly, components of the ionized film forming material in the plasma state are attracted aggressively to the substrate, so that a thin film such as a silicon oxide insulating film can be formed on the substrate. More specifically, when forming a shallow trench isolation (STI) region on a substrate, a thin film of a silicon oxide film (SiO2 film) is formed in a recess formed in a surface layer of the substrate by using a high density plasma (HDP) type CVD apparatus.
When burying the recess formed in the surface layer of the substrate or above the substrate by a plasma CVD apparatus, the following phenomenon is observed in the recess of the edge area of the substrate in the midst of burying. After a film of SiO2 once depositing on the upper side of the recess, for example, in a certain portion of an inner wall of the recess near the opening of the recess, is mostly peeled off by the sputtering action of the plasma CVD apparatus, the film deposits again at a portion opposite to the portion of the inner wall of the recess. That is, when the SiO2 film is formed by using the plasma CVD apparatus, deposition of the SiO2 film and sputtering take place in parallel. As a result, an overhang portion formed of the SiO2 film is formed near the opening of the recess in the burying. The overhang portion grows along with the progress of the SiO2 film forming process, that is, the recess burying process, until the opening of the recess is closed. Thus, the overhang portion formed near the opening of the recess is a cause of formation of voids in the recess. In other words, the overhang portion near the opening of the recess causes to lower the burying characteristic of the recess in the edge area of the substrate.
In the edge area of the substrate, most voids formed in the recess after burying of the recess are asymmetrical to the radial direction of the recess in a longitudinal view. This is because the material gas in the edge area of the substrate is different from the center part of the substrate in the incident direction into the recess. More specifically, in the edge area of the substrate, components of ionized material gas in the plasma state enter the recess obliquely from above toward the radial outer side of the substrate from the center part side of the substrate. Such incidence of the material gas into the recess obliquely from above is a cause of forming easily the overhang portion near the opening of the recess in the edge area of the substrate. It is also one of the causes of lowering the burying characteristic of the recess in the edge area of the substrate. In the central part of the substrate, meanwhile, such a problem hardly occurs because the material gas enters the recess substantially from right above. Thus, when burying the recess formed in the substrate or above the substrate with a thin film by using a plasma CVD apparatus, generally, the burying characteristic is poor in the edge area of the substrate as compared with the central part of the substrate.
Further, when voids are formed in the recess, the quality, performance and yield of the semiconductor substrate are lowered, and the manufacturing cost soars. As a result, the quality, performance and yield of the semiconductor device having such a semiconductor substrate are lowered, and the manufacturing cost hikes up.